Use AutoCXX also for mock

[theHamsta]

With dynamic loading, the real implementation also compiles and runs on MacOS (just fails on dynamic loading because of missing TRT libs). We should use the generated types from autocxx also in the mock.

With #19 finished, we might implement mock by just having one real implementation with function bodies conditionally compiled out and with PhantomData<...> in the structs for whatever the real bindings have.